The present invention relates generally to electrical filters which operate at microwave frequencies. More particularly, the present invention relates to resonant cavity filters in which the cavity is filled with a solid dielectric material. Furthermore, the present invention is concerned with tuning such filters and coupling them to microstrip circuits.
Resonant cavity filters are known in the art. However, solid dielectric-filled, resonant cavity filters, are relatively new. The interior of such a filter is filled with a solid material, typically a ceramic which exhibits a high dielectric constant. A relatively thin metallic plating clad to the solid material forms the cavity walls.
Many of the known techniques for coupling to and tuning a resonant cavity filter fail to adequately solve coupling and tuning problems associated with solid filled cavities. For example, coupling and tuning techniques which require penetration of the interior of the cavity with probes or other mechanical parts are undesirable for a ceramic filled cavity because the ceramic material may be extremely hard and difficult to penetrate.
Additionally, many known coupling techniques require the use of intermediate components, such as coaxial cables and connectors, in order to couple a resonant cavity to a microstrip circuit. Thus, improvements are further needed to permit direct coupling between microstrip circuits and resonant cavities. Such improvements lower the cost and improve the reliability associated with using resonant cavities with microstrip circuits.